The administration of isoproterenol causes a marked increase in the activity of protein carboxymethylase and its acceptor protein in rat parotid glands. This stimulation of protein carboxymethylase has been shown to be mediated by a beta-adrenergic receptor. Stimulation of the posterior pituitary by the ingestion of sodium chloride caused an increase in protein carboxymethylase in the posterior pituitary and a decrease of an acceptor protein tentatively identified as neurophysin. Protein carboxymethylase has been found to be highly localized in sperm of rat. In an infertile rat mutant the activity of protein carboxymethylase in markedly diminished.